Field of the Invention
The present invention relates in general to the field of information handling system communication with storage devices, and more particularly to an asymmetric storage device wide link.
Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Effective use of information handling systems typically requires ready access to storage systems for writing and reading information. Generally, storage systems have multiple storage devices to provide redundancy that prevents information loss in the event a particular storage device experiences a failure. For example, storage devices are assembled in storage enclosures supported by a common backplane. The storage devices coordinate communication with other devices that are external to the backplane by communicating through an expander block, such as an SAS Expander Block Wide Link. For example, a typical SAS Expander Block Wide Link connects with each storage device through the backplane and selectively provides access to each storage device through four narrow serial links that act as a single wide link. Each narrow link has a transmit and receive direction so that a storage device interfaced with a narrow link through the expander block can send and receive information. SAS Expander Block connectors can form daisy chain connections so that a series of storage enclosure systems interface through a common set of connectors. Since individual storage devices are typically accessed intermittently, a single wide link connector can typically support a large number of storage devices under normal operating conditions without having excessive delays due to communication channel congestion across a wide link. However, when information technology administrators assemble storage systems, anticipated storage access impacts the number of storage devices that can efficiently be managed through a wide link.
Assembly of plural narrow links into a wide link connector provides symmetrical bandwidth through the wide link because each serial narrow link has a transmit and a receive path that each operate at the same negotiated link speed. In many application environments, the ratio of reads to writes is asymmetric in nature as different tasks call for retrieving or storing information in spurts. An SAS wide link connector allows for aggregation of multiple narrow links to allow four-by link bandwidth up and down, however, in most storage system enclosure designs the total bandwidth that each storage device can consume at any given time is far greater than the bandwidth available through all four narrow links of the wide link connector. Variable bandwidth consumption is especially apparent with solid state drive (SSD) storage devices that have become available as an alternative to hard disk drive (HHD) storage devices. SSD devices tend to have asymmetric read and write behaviors with read performance typically better than write performance. As a result, during normal operations, one-half of available bandwidth through the wide link connector is often underutilized relative to the other half of available bandwidth.